A military doctor employed by Russias GRU intelligence agency was one of the two suspects accused of carrying out the Salisbury nerve agent attack, an investigatory website has claimed.
The two suspects in the attempted assassination of ex-Russian spy Sergei Skripal were originally named by the UK authorities as Ruslan Boshirov and Alexander Petrov – although it was made clear that the names were aliases.
The suspect identified as Petrov was actually Dr Alexander Yevgenyevich Mishkin, the Bellingcat group said.
In a statement, the website said: Bellingcats identification process included multiple open sources, testimony from people familiar with the person, as well as copies of personally identifying documents, including a scanned copy of his passport.
The 39-year-old graduated from one of Russias elite Military Medical Academies, the groups website said.
During his studies he was recruited by the GRU military intelligence agency.
By 2010 had relocated to Moscow, where he received his undercover identity – including a second national ID and travel passport – under the alias Alexander Petrov.
Bellingcat has already identified Boshirov as Colonel Anatoliy Chepiga – a highly-decorated officer in the GRU.
A spokesman for the Home Office said: We are not commenting as this is still a police investigation.
Further details of Bellingcats investigation to unmask Mishkin will be released on Tuesday.
The reported identity is allegedly not disputed by UK security services.
The men identified as Petrov and Boshirov are believed to have smeared the highly toxic Novichok nerve agent on a door handle at the Wiltshire home of Mr Skripal on March 4.
The attack left Mr Skripal and his daughter Yulia critically ill, while Dawn Sturgess, 44, who was later exposed to the same nerve agent, died in July.
The suspects were identified as GRU agents and Theresa May said their actions were not a rogue operation and would have been approved at a senior level in Moscow.
The activities of the GRU have come under further scrutiny after the agency was accused of trying to hack the global chemical weapons watchdog which is investigating the Salisbury nerve agent attack.
Officials in the Netherlands, where the Organisation for the Prohibition of Chemical Weapons (OPCW) is based, said four Russians had been expelled after the alleged cyber strike.
British intelligence helped thwart the operation which was launched in April, a month after the Novichok poisoning.
The GRU has also been blamed for a string of cyber attacks targeting political institutions, businesses, media and sport.
The National Cyber Security Centre (NCSC) said a number of hackers known to have launched attacks have been linked to the GRU.
The NCSC associated four new attacks with the GRU, on top of previous strikes believed to have been conducted by Russian intelligence.
Among targets of the GRU attacks were the World Anti-Doping Agency (Wada), transport systems in Ukraine, and democratic elections, such as the 2016 US presidential race, according to the NCSC.
The centre said it was almost certainly the GRU behind a BadRabbit attack in October 2017 that caused disruption to the Kiev metro, Odessa airport and Russias central bank.